<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>第二个js页面</title>
</head>
<body>
    <script type="text/javascript">
        var a = 10;
        var b = "hello";
        var c = true;
        var d = null;
        var ab = a+b;
        var ac = a+c;
        var bc = b+c;
        var ad = a+d;
        var bd = b+d;
        var cd = c+d;
        console.info("num+str:"+typeof(ab)+":"+ab);
        console.info("num+boolean:"+typeof(ac)+":"+ac);
        console.info("str+boolean:"+typeof(bc)+":"+bc);
        console.info("num+null:"+typeof(ad)+":"+ad);
        console.info("str+null:"+typeof(bd)+":"+bd);
        console.info("boolean+null:"+typeof(cd)+":"+cd);
        /*
        var a;
        var b = 0;
        var c = true;
        var d = "";
        var ab = a+b;
        var ac = a+c;
        var bd = b+d;
        var flag = !!b;
        var flag2 = !!d;
        console.info("a:"+a);
        console.info("b:"+b);
        console.info(typeof(ab)+":"+ab+":"+isNaN(ab));
        console.info(typeof(ac)+":"+ac+":"+isNaN(ac));
        console.info(typeof(bd)+":"+bd+":"+isNaN(bd));
        console.info(typeof(flag)+":"+flag);
        console.info(typeof(flag2)+":"+flag2);
        var s = eval("1+1");
        console.info(typeof(s)+":"+s);
        console.info(1==true);
        console.info(1===true);
         */
    </script>
</body>
</html>